DESCRIPTION: The proposed studies will examine the mechanisms of diethylstilbestrol or DES-induced carcinogenesis in the hamster kidney. The applicant has observed a) mutation in DNA pol b in DES-induced kidney tumors cDNA as well as genomic sequences form tumor DNA PCR products, b) truncated DNA pol b protein in tumors, c) a down-regulation of DNA pol b mRNA expression in the tumors when compared to levels found in normal kidney, and d) a decrease in fidelity of DNA repair in kidney samples derived from DES-treated rats as compared to those obtained from untreated animals. Based on these preliminary findings, the applicant hypothesizes that DES exposure produces mutational changes in the DNA pol b gene which either leads to the synthesis of a dominant negative protein or an enzyme with reduced DNA repair capability. It is further postulated that attenuation or abolition of DNA pol b function induces genomic instability in Syrian hamster kidney cells which, in turn, sets up an environment for more mutational changes in the tissue. In this proposal, the applicant will 1) determine the time at which the mutated DNA pol b appears during the course of evolution of the DES-induced tumors, 2) determine if DNA repair capacity and fidelity in DNA repair are comprised in tumor tissues expressing the mutated DNA pol b gene, and 3) determine if cells transformed with the mutated DNA pol b exhibit a greater degree of genomic instability by analyses of mutations in microsatellites and the WT1 gene.